The paradigm of modern drug discovery is centered on the development of therapies directed against specific pathological cell types or specific molecular targets, particularly components of cell signaling pathways. Anticancer drug discovery, for example, has turned away from searches for non-specific cytotoxic agents, and instead is focused on finding therapies directed against cancer-specific molecular targets, which are often components of complex cell signaling pathways. With this paradigm shift arises the need for new methods of validating the efficacy of these therapeutics against the cellular and molecular targets for which they were developed, and for model systems capable of dissecting the complex molecular interactions occuring in multifactorial signaling pathways.